An adult rot grub is a skittering, yellow arachnid that lives for only a few hours: long enough to lay dozens of eggs on a host corpse. The rot grub young can spend weeks growing when they only have a dead corpse to devour, but can grow to adulthood when there is living tissue to feast upon. The juvenile rot grubs quickly attack any living creatures that approach, burrowing into their flesh, sapping their health, and destroying major organs within a minute. [1]

Usually, small numbers of rot grubs are hazards that occur near the corpse of a humanoid or similarly-sized creature. Occasionally, rot grubs infest the corpse of a mammoth, cloud giant, old dragon, or other huge creature. After the rot grubs devour all the flesh of the enormous carcass, they erupt from the corpse as an enormous swarm that actively seeks creatures to kill and consume. The swarms quickly consume the creatures they kill, as well as any adults that happen to mature. [1]

Rarely, a rot grub will fail to mature to its adult form, especially after devouring dragonflesh. These individuals grow larger as they consume flesh, eventually developing into a halfling-sized grublike predator.[1]